This invention relates generally to a method for making an article having a foamed plastic body and a surface plate and more particularly has reference to a method for making a polyurethane foam water ski having a flush aluminum deck.
The current method for making foamed plastic water skis having aluminum decks is described in U.S. Pat. No. 4,250,585, the disclosure of which is incorporated herein by reference.
The patent describes a reaction injection molding process. A plurality of rods are positioned in a mold cavity by plastic jigs. An aluminum sheet pre-treated to bond to foamed plastic is placed at the mold parting line to close the mold cavity. Foam is injected into the cavity, where it expands and hardens and bonds to the aluminum sheet. The ski blank is removed from the mold and the aluminum top surface is trimmed to the desired shape.
The known process has a number of disadvantages.
The requirement that the aluminum sheet be placed at the mold parting line limits ski design. The ski will necessarily have a flat top surface and will necessarily have a deck which lies on top of the foamed plastic body. Those features detract from the safety and appearance of the product.
Another disadvantage is that costly and labor intensive production steps are needed to trim the deck after molding. Those steps include bandsaw trimming of the aluminum deck top, routing the remaining edge material, and filing the edge for smoothness. The trimming steps also increase the likelihood of product damage during manufacture.
A need thus exists for a process in which a die cut aluminum ski top can be placed in the mold cavity, thereby eliminating all product design limitations and reducing the labor required to trim the ski top.
One obstacle which has heretofore prevented fulfillment of that need is the extreme mold pressures which develop in reaction injection molding. The foam enters the mold in a liquid state. The foam then expands rapidly to fill the mold cavity and produce a dense structural foam body. When attempting to place a pre-cut aluminum top in a mold cavity, a perfect seal must be maintained or the extreme mold pressures will cause the foam material to leak around and distort the aluminum top.
Pertinent U.S. and foreign patents are found in Class 264, subclasses 46.4, 46.7, 46.8, 45.5 and Digest 83; Class 9, subclasses 310 A, 310 E and 310 R; Class 427, subclass 388.1 and Class 441, subclasses 68, 70 and 74 of the official classifications of patents in the U.S. Patent and Trademark Office.
Examples of pertinent patents are U.S. Pat. Nos. 4,046,611; 4,261,778; 2,920,898; 3,173,161; 3,318,609 and 3,928,106.
U.S. Pat. No. 4,046,611 shows a gasket, vacuum forming and polyurethane foam blow molding. However, the patent does not use a plate and does not use a gasket to prevent migration of the foam around the plate.
U.S. Pat. No. 4,261,778 shows a polyurethane foam ski construction. However, the patent does not show an inverted mold cavity, a gasket, or a vacuum-held plate.
The remaining patents are less pertinent and are cited merely to show the state of the art in ski construction.
None of the patents fulfills the above-cited need for a process in which a die cut aluminum ski top can be placed in the mold cavity.